According to a conventional system, plural terminals each execute transmission and reception when the terminals are present in an area enabling the terminals to mutually receive data; each terminal transfers a portion of data that is to be distributed and not retained by the terminal, from a counterpart terminal thereto and retains the portion; the terminal repeats this transfer also with the other terminals; and thereby, the terminal acquires the overall data to be distributed. According to another system, terminals are classified into positional groups; distribution groups are formed from information concerning the positional groups and station distribution performance data; and data distribution is executed at distribution intervals set in advance for each distribution group in a time slot set in advance (see, e.g., Japanese Laid-Open Patent Publication Nos. 2007-81542 and 2006-246090).
However, according to the conventional techniques, when the terminals move, the density of the terminals dynamically varies and therefore, a problem arises in that it is difficult for each of the terminals to acquire all of the necessary data by data transfers among the terminals and data distribution in each group.